1. Field of the Invention
This invention relates generally to the post-manufacture alteration of the properties of an optical device, and, more specifically, to the irradiation of light adjustable lenses.
2. Background Information
Cataract surgery procedures involve making an incision in the anterior lens capsule to remove the cataractous crystalline lens and implanting an intraocular lens (IOL) in its place. In general, there are two types of intraocular lenses. One type replaces the eye's natural lens, usually to replace a cataractous lens. The other type is used to supplement an existing lens and functions as a permanent corrective lens. This type of lens (referred to as a phakic IOL) is implanted in the anterior or posterior chamber to correct refractive errors of the eye. In theory, the power for either type of IOL required for emmetropia (i.e., point focus on the retina from light originating at infinity) can be precisely calculated. The power of the implanted lens is selected based on pre-operative measurements of ocular length and corneal curvature to enable the patient to see without additional corrective measures (e.g., glasses or contact lenses). Unfortunately, due to errors in measurement, and/or variable lens positioning and wound healing, about half of these patients undergoing this procedure will not enjoy optimal vision without correction after surgery (Brandser et al., Acta Opthalmol Scand 75:162-165 (1997); Oshika et al., J Cataract Refract Surg 24:509-514 (1998). Because the power of such IOLs generally cannot be adjusted once they have been implanted, the patient typically must be resigned to the use of additional corrective lenses such as eyeglasses or contact lenses. Rarely is the implanted lens exchanged for one of more appropriate lens power.
An answer to the foregoing problems is a light adjustable lens, which is an optical device whose refractive properties can be changed after its fabrication and insertion into a human eye. Such a lens is described in detail in International Application Ser. No. PCT/US99/41650, filed on Oct. 13, 1999 and published Jul. 20, 2000, the disclosure of which is incorporated herein by this reference. The light adjustable lens has a refraction modulating composition dispersed in a polymer matrix. One to four weeks after the lens has been implanted into the eye and refractive stabilization has occurred, the preexisting optical aberrations or those induced by the surgical procedure are measured. In order to correct these optical aberrations (e.g. spherical power, astigmatism, prism, etc.), a corresponding amount of radiation is applied to the light adjustable lens, which alters the optical properties of the lens either through changes in its shape, its index of refraction, or both. Following one or several irradiations in which portions of the lens have been exposed to selectively and spatially modify the refractive power, the entire lens is irradiated to “lock in” the modified lens.
The irradiation sources that have enough intensity to modify the refractive properties of an implanted, adjustable intraocular lens in situ are either coherent light sources such as a laser, which can potentially cause permanent damage to the retina by creating high intensities focused to a point on the retina, or high power incoherent sources that have to be attenuated by as much as {fraction (1/1000)} in order to avoid damage to the eye. Accordingly, there is a need for an irradiation source to modify an intraocular lens, e.g., in situ after implantation of the lens in the eye.
There is also a need to more accurately modify the lens so as to more closely compensate for remaining aberrations, and a need to assure that locking radiation will irradiate the lens behind the iris in patients where the iris does not fully dilate.